The present invention relates to receive circuits for ultrasound imaging. In particular, receive circuits for use with different transducers are provided.
Ultrasound imaging for echocardiography applications requires transducers with high volume-per-second rates for scanning. For real-time imaging of moving structures, 20 or more, such as 35, two or three-dimensional representations are generated each second. Large amounts of information are communicated from an ultrasound probe to an ultrasound system base unit.
Various transducers and associated beamformers have been provided for three-dimensional ultrasound imaging. Currently, mostly mechanical transducers are used. However, the associated imaging is not provided in real time and typically requires ECG gating. Two-dimensional transducer arrays for faster electronic/electronic steering and volume acquisition also have been provided. For example, sparse two-dimensional arrays or fully sampled two-dimensional arrays have been used. Sparse arrays provide poor contrast resolution.
Fully sampled two-dimensional arrays use expensive additional beamforming hardware. Two-dimensional arrays repetitively generate transmit beams and responsive receive beams. The beams are electronically steered within the three-dimensional volume. Electronic steering requires a system channel for each of the elements used. Since the number of elements in a two-dimensional array is high, the number of channels required is high. More channels require a greater number of cables. Providing beamforming or partial beamforming within the probe of the transducer array may reduce the number of cables required, but the required number of channels and hardware for sampling the two-dimensional array is still high. Furthermore, analog delays used for beamforming in the probe are expensive and large, and the beamformer in the probe may have limited programmability.
Transducer arrays include elements with a ground electrode and a signal electrode switchably connected to separate transmit and receive system channels. With beamforming capabilities built into the probe, high voltage transistors or diodes operating as switches to isolate the transmit channels from the receive channels are also included within the probe. These high voltage devices are not easily integrated with the beamforming circuitry, so require additional space.
In one system disclosed in U.S. Pat. No. 5,622,177, the number of system channels and cables is reduced by using time division multiplexing. Data from a plurality of elements is multiplexed onto one signal line. However, time division multiplexed data has different characteristics than conventional data representing the signal from a single transducer element. Receive circuitry designed for use with conventional data may improperly introduce noise or errors in time division multiplexed data.
By way of introduction, the preferred embodiments described below include methods and systems for isolating transmit and receive circuitry at an ultrasound transducer element. Separate electrodes or electrodes on opposite sides of a transducer element are connected to the separate transmit and receive paths or channels. Instead of high voltage transmit and receive switching, the transducer element isolates the transmit channel from the receive channel. The transmit channel includes circuitry for limiting the voltage at one electrode during receive processing, such as a switch operable to connect the electrode to ground. The receive channel includes circuitry for limiting the voltage at an electrode during transmit processing, such as a diode clamp preventing voltage swings greater than diode voltage at the electrode. Limiting the voltage provides virtual grounding or a direct current for either of the transmit or receive operation.
Using a transmit channel discussed above or other transmit channels, a unipolar pulse may be generated starting at one voltage and ending at a different voltage. For example, a unipolar pulse is generated starting at a zero voltage value and ending on a positive voltage value. A subsequent unipolar pulse is transmitted by starting at the positive voltage value and ending on the zero voltage value. These mirrored unipolar transmit waveforms may be used for phase inversion imaging, such as adding responsive received signals for isolating nonlinear response information.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.